Hello Asian Garden,
As a US citizen, you are still responsible for taxes on any income you earn worldwide, regardless of where you reside. So you should be filing tax returns in the US, even though you reside in Belize.
However, if you live outside of the United States for 330 days in any 12 month consecutive period, you are also eligible to exclude from your income up to $85,700 of your foreign income (that is the current exemption amount). So if your foreign income is less than this amount, then chances are you will not owe any income taxes on your foreign income, however, a return should still be filed.
However, if you own your own business or are self employed, you are still responsible for paying social security and medicare taxes on your earnings, even though those earnings may not be subject to income tax. The current self employment tax rate for self employed individuals is 15.3% of your net income. The US does not have a tax treaty with Belize on social security taxes, so you would not be exempt from the social security and medicare taxes.
If you have not filed your returns for several years, you should do so as soon as possible. Penalties may be assessed for failure to file and also for late filing. Interest will also be accrued on any tax liability that you may have. Even if you cannot afford to pay whatever taxes may be due, you should still file your returns, as it is possible that a payment plan might be worked out by the IRS for you to pay off any tax liability owed for past years.
I am giving you a link to a section of the IRS website that expalins steps you should take for filing past due returns. It will also include links to web pages and phone numbers you can call to obtain help from the IRS in filing these returns.
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Thank you and good luck in getting this resolved.